The invention relates to a heating arrangement for an installation producing corrugated cardboard. More particularly, the heating arrangement includes several heating plates arranged successively in the direction of movement of a corrugated cardboard web and at least one pressure unit consisting of a bearing, arranged diagonally with respect to the direction of advance of the corrugated cardboard web at which at least one pressure element is attached.
Such a device in an installation producing corrugated cardboard has the task of drying glue between superposed webs, that is, one-sided corrugated cardboard webs and finally the cover web.
For this purpose, a known arrangement has heating plates which are heated, for example, with the vapor of a thermo-oil. With the aid of a pressure unit and its driven lower belt, a conveyor belt moves the corrugated cardboard webs to be glued along the surface of the heating plates. Load elements press the corrugated cardboard webs against the surfaces of the heating plates in order to achieve an appropriate contact of the corrugated cardboard web with the heating plate surface, that is, in order to achieve a good heat transfer toward the gluing line.
As pressure units, several systems are known. For example, pressure units may use tension rollers, a pressure hood operating with compressed air, elements which rest directly on the conveyor belt due to their own weight, or plates which are pressed against the conveyor belt by means of a spring force.
When pressure hoods such as that shown in European Patent Publication 0 412 255 A1 are used, an additional energy output for the compressed air is necessary in order to press the pressure hood onto the corrugated cardboard web. Furthermore, a certain noise level occurs in the drying area. Moreover, heat energy is unnecessarily transported and the adjustment of the working width is costly.
In the case of systems where elements press with their own weight on the belt, such as shown in European Patent publication 0 559 181 A1, no damping effect is present so that significant dynamic forces can occur. The load elements are at a relatively great distance from the friction surface so that the friction moment can become relatively great. Moreover, the load elements are subjected to a tendency toward turning which may lead to a deterioration of uniform surface contact with the heating plate surface.
The state of the art also includes to a pressure unit in which lower plates are pressured via compressed air chambers, as shown in U.S. Pat. No. 5,526,739. The construction of this known device is costly and the device also has the disadvantage that the pressure is not uniformly applied.
Canadian Patent No. 2,179,921 shows a pressure unit in the form of a load plate which consists of several units extending along the corrugated cardboard web. With this system, the corrugated cardboard web is pressured directly, possibly resulting in undesirable damage.
Another known pressure unit uses tension rollers which are attached via intermediate levers at a bearing arranged diagonally with respect to the direction of advance of the corrugated cardboard web as shown in U.S. Pat. No. 5,632,830. However, uniform pressure on the corrugated cardboard web is not assured with this system.
Moreover, in the case of pressure units with tension rollers, the rollers must not cause any jolts, oscillations or vibrations which could damage the corrugated cardboard web. During operation, it is also necessary for the tension rollers and the heating plates to be almost perfectly level so that an appropriate contact of the corrugated cardboard web and the heating plates can be realized.
From the state of the art on which the present invention is based, European Patent publication 0 623 459 B1 shows a system in which a spring force is applied to plates. This system also uses a conveyor belt. Each pressure plate is mounted to a rigid traverse via a double-jointed lever system, so that the pressure plate undergoes a plane, parallel movement. The pressure plate is pressured via spring elements.
With this known system, it is disadvantageous that the pressure plate is not always aligned parallel with the heating surface due to possible mounting deviations and/or unevennesses of the heating surface. An additional disadvantage is that the spring deflection and therefore also the pressing force change with variation of the corrugated cardboard thickness. It is necessary to adjust the tension of each pressure plate in accordance with the corrugated cardboard type used.